Fuel cell module

ABSTRACT

A fuel cell module includes a first area where an exhaust gas combustor and a start-up combustor are provided, an annular second area around the first area and where a reformer and an evaporator are provided, an annular third area around the second area and where a heat exchanger is provided, and an annular heat recovery area around the third area as a passage of oxygen-containing gas for recovery of heat radiated from the third area toward the outer circumference.

TECHNICAL FIELD

The present invention relates to a fuel cell module including a fuelcell stack formed by stacking a plurality of fuel cells for generatingelectricity by electrochemical reactions of a fuel gas and anoxygen-containing gas.

BACKGROUND ART

Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte ofion-conductive solid oxide such as stabilized zirconia. The solidelectrolyte is interposed between an anode and a cathode to form anelectrolyte electrode assembly (hereinafter also referred to as MEA).The electrolyte electrode assembly is sandwiched between separators(bipolar plates). In use, generally, predetermined numbers of theelectrolyte electrode assemblies and the separators are stacked togetherto form a fuel cell stack.

As a system including this type of fuel cell stack, for example, a fuelcell battery disclosed in Japanese Laid-Open Patent Publication No.2001-236980 (hereinafter referred to as the conventional technique 1) isknown. As shown in FIG. 10, the fuel cell battery includes a fuel cellstack la, and a heat insulating sleeve 2 a is provided at one end of thefuel cell stack la. A reaction device 4 a is provided in the heatinsulating sleeve 2 a. The reaction device 4 a includes a heat exchanger3 a.

In the reaction device 4 a, as a treatment of liquid fuel, partialoxidation reforming which does not use water is performed. After theliquid fuel is evaporated by an exhaust gas, the liquid fuel passesthrough a feeding point 5 a which is part of the heat exchanger 3 a. Thefuel contacts an oxygen carrier gas heated by the exhaust gas thereby toinduce partial oxidation reforming, and then, the fuel is supplied tothe fuel cell stack 1 a.

Further, as shown in FIG. 11, a solid oxide fuel cell disclosed inJapanese Laid-Open Patent Publication No. 2010-504607 (PCT) (hereinafterreferred to as the conventional technique 2) has a heat exchanger 2 bincluding a cell core 1 b. The heat exchanger 2 b heats the cathode airutilizing waste heat.

Further, as shown in FIG. 12, a fuel cell system disclosed in JapaneseLaid-Open Patent Publication No. 2004-288434 (hereinafter referred to asthe conventional technique 3) includes a first area is having a circularcylindrical shape extending vertically, and an annular second area 2 caround the first area 1 c, an annular third area 3 c around the secondarea 2 c, and an annular fourth area 4 c around the third area 3 c.

A burner 5 c is provided in the first area 1 c, and a reforming pipe 6 cis provided in the second area 2 c. A water evaporator 7 c is providedin the third area 3 c, and a CO shift converter 8 c is provided in thefourth area 4 c.

SUMMARY OF INVENTION

In the conventional technique 1, at the time of reforming by partialoxidation in the reaction device 4 a, heat of the exhaust gas is usedfor heating the liquid fuel and the oxygen carrier gas. Therefore, thequantity of heat for raising the temperature of the oxygen-containinggas supplied to the fuel cell stack 1 a tends to be inefficient, and theefficiency is low.

Further, in the conventional technique 2, in order to increase heatefficiency, long flow channels are adopted to have a sufficient heattransmission area. Therefore, considerably high pressure losses tend tooccur.

Further, in the conventional technique 3, radiation of the heat from thecentral area having the highest temperature is suppressed using heatinsulation material (partition wall). Therefore, heat cannot berecovered, and the efficiency is low.

The present invention has been made to solve the problems of this type,and an object of the present invention is to provide a fuel cell modulehaving simple and compact structure in which it is possible to achieveimprovement in the heat efficiency and facilitation of thermallyself-sustaining operation.

The present invention relates to a fuel cell module including a fuelcell stack formed by stacking a plurality of fuel cells for generatingelectricity by electrochemical reactions of a fuel gas and anoxygen-containing gas, a reformer for reforming a mixed gas of a rawfuel chiefly containing hydrocarbon and water vapor to produce the fuelgas supplied to the fuel cell stack, an evaporator for evaporatingwater, and supplying the water vapor to the reformer, a heat exchangerfor raising the temperature of the oxygen-containing gas by heatexchange with a combustion gas, and supplying the oxygen-containing gasto the fuel cell stack, an exhaust gas combustor for combusting the fuelgas discharged from the fuel cell stack as a fuel exhaust gas and theoxygen-containing gas discharged from the fuel cell stack as anoxygen-containing exhaust gas to produce the combustion gas, and astart-up combustor for combusting the raw fuel and the oxygen-containinggas to produce the combustion gas.

The fuel cell module includes a first area where the exhaust gascombustor and the start-up combustor are provided, an annular secondarea around the first area and where the reformer and the evaporator areprovided, an annular third area around the second area and where theheat exchanger is provided, and an annular heat recovery area around thethird area as a passage of fluid for recovery of heat radiated from thethird area toward an outer circumference of the fuel cell module.

In the present invention, the first area including the exhaust gascombustor and the start-up combustor is centrally-located. The annularsecond area is successively provided around the first area, and theannular third area is then provided around the second area. The reformerand the evaporator are provided in the second area, and the heatexchanger is provided in the third area.

In the structure, heat waste and heat radiation are suppressed suitably.Thus, improvement in the heat efficiency is achieved, and thermallyself-sustaining operation is facilitated. Further, simple and compactstructure is achieved in the entire fuel cell module. The thermallyself-sustaining operation herein means operation where the operatingtemperature of the fuel cell is maintained using only heat energygenerated by the fuel cell itself, without supplying additional heatfrom the outside.

Further, heat insulation effect for suppressing heat radiation and heatwaste is achieved in the annular heat recovery area around the thirdarea. Thus, improvement in the heat efficiency is achieved, andthermally self-sustaining operation is facilitated.

The above and other objects features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing structure of a fuel cellsystem including a fuel cell module according to a first embodiment ofthe present invention;

FIG. 2 is a perspective view showing FC peripheral equipment of the fuelcell module;

FIG. 3 is a cross sectional view showing the FC peripheral equipment;

FIG. 4 is a perspective view with partial omission showing the FCperipheral equipment;

FIG. 5 is an exploded perspective view showing main components of the FCperipheral equipment;

FIG. 6 is a cross sectional view showing the FC peripheral equipment;

FIG. 7 is a view showing an evaporation return pipe of the FC peripheralequipment;

FIG. 8 is a diagram schematically showing structure of a fuel cellsystem including a fuel cell module according to a second embodiment ofthe present invention;

FIG. 9 is a cross sectional view showing FC peripheral equipment of thefuel cell module;

FIG. 10 is a view schematically showing a fuel cell battery disclosed ina conventional technique 1;

FIG. 11 is a perspective view with partial cutout showing a solid oxidefuel cell disclosed in a conventional technique 2; and

FIG. 12 is a view schematically showing a fuel cell system disclosed ina conventional technique 3.

DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1, a fuel cell system 10 includes a fuel cell module 12according to a first embodiment of the present invention, and the fuelcell system 10 is used in various applications, including stationary andmobile applications. For example, the fuel cell system 10 is mounted ona vehicle.

The fuel cell system 10 includes the fuel cell module (SOFC module) 12for generating electrical energy in power generation by electrochemicalreactions of a fuel gas (a gas produced by mixing a hydrogen gas,methane, and carbon monoxide) and an oxygen-containing gas (air), a rawfuel supply apparatus (including a fuel gas pump) 14 for supplying a rawfuel (e.g., city gas) to the fuel cell module 12, an oxygen-containinggas supply apparatus (including an air pump) 16 for supplying theoxygen-containing gas to the fuel cell module 12, a water supplyapparatus (including a water pump) 18 for supplying water to the fuelcell module 12, and a control device 20 for controlling the amount ofelectrical energy generated in the fuel cell module 12.

The fuel cell module 12 includes a solid oxide fuel cell stack 24 formedby stacking a plurality of solid oxide fuel cells 22 in a verticaldirection (or horizontal direction). The fuel cell 22 includes anelectrolyte electrode assembly (MEA) 32. The electrolyte electrodeassembly 32 includes a cathode 28, an anode 30, and an electrolyte 26interposed between the cathode 28 and the anode 30. For example, theelectrolyte 26 is made of ion-conductive solid oxide such as stabilizedzirconia.

A cathode side separator 34 and an anode side separator 36 are providedon both sides of the electrolyte electrode assembly 32. Anoxygen-containing gas flow field 38 for supplying the oxygen-containinggas to the cathode 28 is formed in the cathode side separator 34, and a.fuel gas flow field 40 for supplying the fuel gas to the anode 30 isformed in the anode side separator 36. As the fuel cell 22, varioustypes of conventional SOFCs can be adopted.

The operating temperature of the fuel cell 22 is high, that is severalhundred ° C. Methane in the fuel gas is reformed at the anode 30 toobtain hydrogen and CO, and the hydrogen and CO are supplied to aportion of the electrolyte 26 adjacent to the anode 30.

An oxygen-containing gas supply passage 42 a, an oxygen-containing gasdischarge passage 42 b, a fuel gas supply passage 44 a, and a fuel gasdischarge passage 44 b extend through the fuel cell stack 24. Theoxygen-containing gas supply passage 42 a is connected to an inlet ofeach oxygen-containing gas flow field 38, the oxygen-containing gasdischarge passage 42 b is connected to an outlet of eachoxygen-containing gas flow field 38, the fuel gas supply passage 44 a isconnected to an inlet of each fuel gas flow field 40, and the fuel gasdischarge passage 44 b is connected to an outlet of each fuel gas flowfield 40.

The fuel cell module 12 includes a reformer 46 for reforming a mixed gasof a raw fuel chiefly containing hydrocarbon (e.g., city gas) and watervapor to produce a fuel gas supplied to the fuel cell stack 24, anevaporator 48 for evaporating water and supplying the water vapor to thereformer 46, a heat exchanger 50 for raising the temperature of theoxygen-containing gas by heat exchange with a combustion gas, andsupplying the oxygen-containing gas to the fuel cell stack 24, anexhaust gas combustor 52 for combusting the fuel gas discharged from thefuel cell stack 24 as a fuel exhaust gas and the oxygen-containing gasdischarged from the fuel cell stack 24 as an oxygen-containing exhaustgas to produce the combustion gas, and a start-up combustor 54 forcombusting the raw fuel and the oxygen-containing gas to produce thecombustion gas.

Basically, the fuel cell module 12 is made up of the fuel cell stack 24and FC (fuel cell) peripheral equipment (BOP) 56 (see FIGS. 1 and 2).The FC peripheral equipment 56 includes the reformer 46, the evaporator48, the heat exchanger 50, the exhaust gas combustor 52, and thestart-up combustor 54.

As shown in FIGS. 3 to 5, the FC peripheral equipment 56 includes afirst area R1 where the exhaust gas combustor 52 and the start-upcombustor 54 are provided, an annular second area R2 formed around thefirst area R1 and where the reformer 46 and the evaporator 48 areprovided, an annular third area R3 formed around the second area R2 andwhere the heat exchanger 50 is provided. A cylindrical outer member 55constituting an outer wall is provided on the outer peripheral side ofthe third area R3 to form a heat recovery area described later.

The start-up combustor 54 includes an air supply pipe 57 and a raw fuelsupply pipe 58. The start-up combustor 54 has an ejector function, andgenerates negative pressure in the raw fuel supply pipe 58 by the flowof the air supplied from the air supply pipe 57 for sucking the rawfuel.

The exhaust gas combustor 52 is spaced away from the start-up combustor54, and includes a combustion cup 60 formed in a shape of a cylinderhaving a bottom. A plurality of holes (e.g., circular holes orrectangular holes) 60 a are formed along the outer circumference of themarginal end of the combustion cup 60 on the bottom side. A stackattachment plate 62 is engaged with the other end of the combustion cup60 on the opening side. The fuel cell stack 24 is attached to the stackattachment plate 62.

One end of an oxygen-containing exhaust gas channel 63 a and one end ofa fuel exhaust gas channel 63 b are provided at the combustion cup 60.The combustion gas is produced inside the combustion cup 60 bycombustion reaction of the fuel gas (more specifically, fuel exhaustgas) and the oxygen-containing gas (more specifically, oxygen-containingexhaust gas).

As shown in FIG. 1, the other end of the oxygen-containing exhaust gaschannel 63 a is connected to the oxygen-containing gas discharge passage42 b of the fuel cell stack 24, and the other end of the fuel exhaustgas channel 63 b is connected to the fuel gas discharge passage 44 b ofthe fuel cell stack 24.

As shown in FIGS. 3 to 5, the reformer 46 is a preliminary reformer forreforming higher hydrocarbon (C₂+) such as ethane (C₂H₆), propane(C₃H₈), and butane (C₄H₁₀) in the city gas (raw fuel) to produce thefuel gas chiefly containing methane (CH₄), hydrogen, and CO by steamreforming. The operating temperature of the reformer 46 is set atseveral hundred ° C.

The reformer 46 includes a plurality of reforming pipes (heattransmission pipes) 66 provided around the exhaust gas combustor 52 andthe start-up combustor 54. Each of the reforming pipes 66 is filled withreforming catalyst pellets (not shown). Each of the reforming pipes 66has one end (lower end) fixed to a first lower ring member 68 a, and theother end (upper end) fixed to a first upper ring member 68 b.

The outer circumferential portions of the first lower ring member 68 aand the first upper ring member 68 b are fixed to the innercircumferential portion of a cylindrical member 70 by welding or thelike. The inner circumferential portions of the first lower ring member68 a and the first upper ring member 68 b are fixed to the outercircumferential portions of the exhaust gas combustor 52 and thestart-up combustor 54 by welding or the like. The cylindrical member 70extends in an axial direction indicated by an arrow L, and an end of thecylindrical member 70 adjacent to the fuel cell stack 24 is fixed to thestack attachment plate 62. A plurality of openings 72 are formed in theouter circumference of the cylindrical member 70 in a circumferentialdirection at predetermined height positions.

The evaporator 48 has evaporation pipes (heat transmission pipes) 74provided adjacent to, and outside the reforming pipes 66 of the reformer46. As shown in FIG. 6, the reforming pipes 66 are arranged at equalintervals on a virtual circle, concentrically around the first area R1.

The evaporation pipes 74 are arranged at equal intervals on a virtualcircle, concentrically around the first area R1. The number of theevaporation pipes 74 is half of the number of the reforming pipes 66.The evaporation pipes 74 are positioned on the back side of every otherposition of the reforming pipe 66 (i.e., at positions spaced away fromthe center of the first area R1).

As shown in FIGS. 3 and 4, each of the evaporation pipes 74 has one end(lower end) which is fixed to a second lower ring member 76 a by weldingor the like, and the other end (upper end) which is fixed to a secondupper ring member 76 b by welding or the like. The outer circumferentialportions of the second lower ring member 76 a and the second upper ringmember 76 b are fixed to the inner circumferential portion of thecylindrical member 70 by welding or the like.

The inner circumferential portions of the second lower ring member 76 aand the second upper ring member 76 b are fixed to the outercircumferential portions of the exhaust gas combustor 52 and thestart-up combustor 54 by welding or the like.

The second lower ring member 76 a is positioned below the first lowerring member 68 a (i.e., outside the first lower ring member 68 a in theaxial direction), and the second upper ring member 76 b is positionedabove the first upper ring member 68 b (i.e., outside the first upperring member 68 b in the axial direction).

An annular mixed gas supply chamber 78 a is formed between the firstlower ring member 68 a and the second lower ring member 76 a, and amixed gas of raw fuel and water vapor is supplied to the mixed gassupply chamber 78 a. Further, an annular fuel gas discharge chamber 78 bis formed between the first upper ring member 68 b and the second upperring member 76 b, and the produced fuel gas (reformed gas) is dischargedto the fuel gas discharge chamber 78 b. Both ends of each of thereforming pipes 66 are opened to the mixed gas supply chamber 78 a andthe fuel gas discharge chamber 78 b.

A ring shaped end ring member 80 is fixed to an end of the cylindricalmember 70 on the start-up combustor 54 side by welding or the like. Anannular water supply chamber 82 a is formed between the end ring member80 and the second lower ring member 76 a, and water is supplied to thewater supply chamber 82 a. An annular water vapor discharge chamber 82 bis formed between the second upper ring member 76 b and the stackattachment plate 62, and water vapor is discharged to the water vapordischarge chamber 82 b. Both ends of each of the evaporation pipes 74are opened to the water supply chamber 82 a and the water vapordischarge chamber 82 b.

The fuel gas discharge chamber 78 b and the water vapor dischargechamber 82 b are provided in a double deck manner, and the fuel gasdischarge chamber 78 b is provided on the inner side with respect to thewater vapor discharge chamber 82 b (i.e., below the water vapordischarge chamber 82 b). The mixed gas supply chamber 78 a and the watersupply chamber 82 a are provided in a double deck manner, and the mixedgas supply chamber 78 a is provided on the inner side with respect tothe water supply chamber 82 a (i.e., above the water supply chamber 82a).

A raw fuel supply channel 84 is opened to the mixed gas supply chamber78 a, and an evaporation return pipe 90 described later is connected toa position in the middle of the raw fuel supply channel 84 (see FIG. 1).The raw fuel supply channel 84 has an ejector function, and generatesnegative pressure by the flow of the raw fuel for sucking the watervapor.

The raw fuel supply channel 84 is fixed to the second lower ring member76 a and the end ring member 80 by welding or the like. One end of afuel gas channel 86 is connected to the fuel gas discharge chamber 78 b,and the other end of the fuel gas channel 86 is connected to the fuelgas supply passage 44 a of the fuel cell stack 24 (see FIG. 1). The fuelgas channel 86 is fixed to the second upper ring member 76 b by weldingor the like, and extends through the stack attachment plate 62 (see FIG.2).

A water channel 88 is connected to the water supply chamber 82 a. Thewater channel 88 is fixed to the end ring member 80 by welding or thelike. One end of the evaporation return pipe 90 formed by at least oneevaporation pipe 74 is provided in the water vapor discharge chamber 82b, and the other end of the evaporation return pipe 90 is connected to aposition in the middle of the raw fuel supply channel 84 (see FIG. 1).

As shown in FIG. 7, the evaporation return pipe 90 has dual pipestructure 92 in a portion thereof passing through the mixed gas supplychamber 78 a and the water supply chamber 82 a. The dual pipe structure92 includes an outer pipe 94. The outer pipe 94 surrounds theevaporation return pipe 90, and the outer pipe 94 is positionedcoaxially with the evaporation return pipe 90. The outer pipe 94 isfixed to the first lower ring member 68 a, the second lower ring member76 a, and the end ring member 80 by welding or the like, and extends inthe direction indicated by an arrow L. A gap is provided between theouter circumference of the evaporation return pipe 90 and the innercircumference of the outer pipe 94. This gap may not be provided.

The evaporation return pipe 90 may have dual pipe structure 92 a in aportion thereof passing through the fuel gas discharge chamber 78 b. Thedual pipe structure 92 a includes an outer pipe 94 a. The outer pipe 94a surrounds the evaporation return pipe 90, and the outer pipe 94 a ispositioned coaxially with the evaporation return pipe 90. The outer pipe94 a is fixed to the first upper ring member 68 b and the second upperring member 76 b by welding or the like, and extends in the directionindicated by the arrow L.

A gap is formed between the outer circumference of the evaporationreturn pipe 90 and the inner circumference of the outer pipe 94 a asnecessary. The lower end of the outer pipe 94 a is not welded to thefirst upper ring member 68 b.

As shown in FIGS. 3 and 4, the heat exchanger 50 includes a plurality ofheat exchange pipes (heat transmission pipes) 96 which are providedalong and around the outer circumference of the cylindrical member 70.Each of the heat exchange pipes 96 has one end (lower end) fixed to alower ring member 98 a, and the other end (upper end) fixed to an upperring member 98 b.

A lower end ring member 100 a is provided below the lower ring member 98a, and an upper end ring member 100 b is provided above the upper ringmember 98 b. The lower end ring member 100 a and the upper end ringmember 100 b are fixed to the outer circumference of the cylindricalmember 70 and the inner circumference of the outer member 55 by weldingor the like.

An annular oxygen-containing gas supply chamber 102 a to which theoxygen-containing gas is supplied is formed between the lower ringmember 98 a and the lower end ring member 100 a. An annularoxygen-containing gas discharge chamber 102 b is formed between theupper ring member 98 b and the upper end ring member 100 b. The heatedoxygen-containing gas is discharged to the oxygen-containing gasdischarge chamber 102 b. Both ends of each of the heat exchange pipes 96are fixed to the lower ring member 98 a and the upper ring member 98 bby welding or the like, and opened to the oxygen-containing gas supplychamber 102 a and the oxygen-containing gas discharge chamber 102 b.

The mixed gas supply chamber 78 a and the water supply chamber 82 a areplaced on the radially inward side relative to the inner circumferenceof the oxygen-containing gas supply chamber 102 a. The oxygen-containinggas discharge chamber 102 b is provided outside the fuel gas dischargechamber 78 b at a position offset downward from the fuel gas dischargechamber 78 b.

A cylindrical cover member 104 is fixed to the outer circumferentialportion of the outer member 55. The center of the cylindrical covermember 104 is shifted downward.

Both of upper and lower ends (both of axial ends) of the cover member104 are welded to the outer member 55, and a heat recovery area(chamber) 106 is formed between the cover member 104 and the outercircumferential portion of the outer member 55. The heat recovery area106 is provided on the lower side in the axial direction of the FCperipheral equipment 56.

A plurality of holes 108 are formed circumferentially in a lowermarginal end portion of the outer member 55 of the oxygen-containing gassupply chamber 102 a, and the oxygen-containing gas supply chamber 102 acommunicates with the heat recovery area 106 through the holes 108. Anoxygen-containing gas supply pipe 110 communicating with the heatrecovery area 106 is connected to the cover member 104. An exhaust gaspipe 112 communicating with the third area R3 is connected to an upperportion of the outer member 55.

For example, one end of each of two oxygen-containing gas pipes 114 isprovided in the oxygen-containing gas discharge chamber 102 b. Each ofthe oxygen-containing gas pipes 114 has a stretchable member such as abellows 114 a between the upper end ring member 100 b and the stackattachment plate 62. The other end of each of the oxygen-containing gaspipes 114 extends through the stack attachment plate 62, and isconnected to the oxygen-containing gas supply passage 42 a of the fuelcell stack 24 (see FIG. 1).

As shown in FIG. 3, a first combustion gas channel 116 a as a passage ofthe combustion gas is formed in the first area R1, and a secondcombustion gas channel 116 b as a passage of the combustion gas that haspassed through the holes 60 a is formed in the second area R2. A thirdcombustion gas channel 116 c as a passage of the combustion gas that haspassed through the openings 72 is formed in the third area R3. Further,a fourth combustion gas channel 116 d is formed as a passage after theexhaust gas pipe 112. The second combustion gas channel 116 b forms thereformer 46 and the evaporator 48, and the third combustion gas channel116 c forms the heat exchanger 50.

As shown in FIG. 1, the raw fuel supply apparatus 14 includes a raw fuelchannel 118. The raw fuel channel 118 is branched into the raw fuelsupply channel 84 and the raw fuel supply pipe 58 through a raw fuelregulator valve 120. A desulfurizer 122 for removing sulfur compounds inthe city gas (raw fuel) is provided in the raw fuel supply channel 84.

The oxygen-containing gas supply apparatus 16 includes anoxygen-containing gas channel 124. The oxygen-containing gas channel 124is branched into the oxygen-containing gas supply pipe 110 and the airsupply pipe 57 through an oxygen-containing gas regulator valve 126. Thewater supply apparatus 18 is connected to the evaporator 48 through thewater channel 88.

Operation of the fuel cell system 10 will be described below.

At the time of starting operation of the fuel cell system 10, the air(oxygen-containing gas) and the raw fuel are supplied to the start-upcombustor 54. More specifically, by operation of the air pump, the airis supplied to the oxygen-containing gas channel 124. By adjusting theopening degree of the oxygen-containing gas regulator valve 126, the airis supplied to the air supply pipe 57.

In the meanwhile, in the raw fuel supply apparatus 14, by operation ofthe fuel gas pump, for example, raw fuel such as the city gas(containing CH₄, C₂H₆, C₃H₈, C₄H₁₀) is supplied to the raw fuel channel118. By regulating the opening degree of the raw fuel regulator valve120, the raw fuel is supplied into the raw fuel supply pipe 58. The rawfuel is mixed with the air, and supplied into the start-up combustor 54(see FIGS. 3 and 4).

Thus, the mixed gas of the raw fuel and the air is supplied into thestart-up combustor 54, and the mixed gas is ignited to start combustion.Therefore, the combustion gas produced in combustion flows from thefirst area R1 to the second area R2. Further, the combustion gas issupplied to the third area R3, and then, the combustion gas isdischarged to the outside of the fuel cell module 12 through the exhaustgas pipe 112.

As shown in FIGS. 3 and 4, the reformer 46 and the evaporator 48 areprovided in the second area R2, and the heat exchanger 50 is provided inthe third area R3. Thus, the combustion gas discharged from the firstarea R1 first heats the reformer 46, next heats the evaporator 48, andthen heats the heat exchanger 50.

Then, after the temperature of the fuel cell module 12 is raised to apredetermined temperature, the air (oxygen-containing gas) is suppliedto the heat exchanger 50, and the mixed gas of the raw fuel and thewater vapor is supplied to the reformer 46.

More specifically, as shown in FIG. 1, the opening degree of theoxygen-containing gas regulator valve 126 is adjusted such that the flowrate of the air supplied to the oxygen-containing gas supply pipe 110 isincreased, and the opening degree of the raw fuel regulator valve 120 isadjusted such that the flow rate of the raw fuel supplied to the rawfuel supply channel 84 is increased. Further, by operation of the watersupply apparatus 18, the water is supplied to the water channel 88.

The air supplied to the oxygen-containing gas supply pipe 110 flows intothe heat recovery area 106. Thereafter, as shown in FIGS. 3 and 4, theair flows through the holes 108, and the air is supplied to theoxygen-containing gas supply chamber 102 a of the heat exchanger 50.After the air is temporarily supplied to the oxygen-containing gassupply chamber 102 a, while the air is moving inside the heat exchangepipes 96, the air is heated by heat exchange with the combustion gassupplied into the third area R3.

After the heated air is temporarily supplied to the oxygen-containinggas discharge chamber 102 b, the air is supplied to theoxygen-containing gas supply passage 42 a of the fuel cell stack 24through the oxygen-containing gas pipes 114 (see FIG. 1). In the fuelcell stack 24, the heated air flows along the oxygen-containing gas flowfield 38, and the air is supplied to the cathode 28.

After the air flows through the oxygen-containing gas flow field 38, theair is discharged from the oxygen-containing gas discharge passage 42 binto the oxygen-containing exhaust gas channel 63 a. Theoxygen-containing exhaust gas channel 63 a is opened to the combustioncup 60 of the exhaust gas combustor 52, and the oxygen-containingexhaust gas is supplied into the combustion cup 60.

Further, as shown in FIG. 1, the water from the water supply apparatus18 is supplied to the evaporator 48. After the raw fuel is desulfurizedin the desulfurizer 122, the raw fuel flows through the raw fuel supplychannel 84, and moves toward the reformer 46.

In the evaporator 48, after the water is temporarily supplied to thewater supply chamber 82 a, while water is moving inside the evaporationpipes 74, the water is heated by the combustion gas flowing through thesecond area R2, and vaporized. After the water vapor flows into thewater vapor discharge chamber 82 b, the water vapor is supplied to theevaporation return pipe 90 connected to the water vapor dischargechamber 82 b. Thus, the water vapor flows inside the evaporation returnpipe 90, and flows into the raw fuel supply channel 84. Then, the watervapor is mixed with the raw fuel supplied by the raw fuel supplyapparatus 14 to produce the mixed gas.

The mixed gas from the raw fuel supply channel 84 is temporarilysupplied to the mixed gas supply chamber 78 a of the reformer 46. Themixed gas moves inside the reforming pipes 66. In the meanwhile, themixed gas is heated by the combustion gas flowing through the secondarea R2, and is then steam-reformed. After removal (reforming) ofhydrocarbon of C₂₊, a reformed gas chiefly containing methane isobtained.

After this reformed gas is heated, the reformed gas is temporarilysupplied to the fuel gas discharge chamber 78 b as the fuel gas.Thereafter, the fuel gas is supplied to the fuel gas supply passage 44 aof the fuel cell stack 24 through the fuel gas channel 86 (see FIG. 1).In the fuel cell stack 24, the heated fuel gas flows along the fuel gasflow field 40, and the fuel gas is supplied to the anode 30. In themeanwhile, the air is supplied to the cathode 28. Thus, electricity isgenerated in the electrolyte electrode assembly 32.

After the fuel gas flows through the fuel gas flow field 40, the fuelgas is discharged from the fuel gas discharge passage 44 b to the fuelexhaust gas channel 63 b. The fuel exhaust gas channel 63 b is opened tothe inside of the combustion cup 60 of the exhaust gas combustor 52, andthe fuel exhaust gas is supplied into the combustion cup 60.

Under the heating operation by the start-up combustor 54, when thetemperature of the fuel gas in the exhaust gas combustor 52 exceeds theself-ignition temperature, combustion of the oxygen-containing exhaustgas and the fuel exhaust gas is started inside the combustion cup 60. Inthe meanwhile, combustion operation by the start-up combustor 54 isstopped.

The combustion cup 60 has the holes 60 a. Therefore, as shown in FIG. 3,the combustion gas supplied into the combustion cup 60 flows through theholes 60 a from the first area R1 into the second area R2. Then, afterthe combustion gas is supplied to the third area R3, the combustion gasis discharged to the outside of the fuel cell module 12.

In the first embodiment, the FC peripheral equipment 56 includes thefirst area R1 where the exhaust gas combustor 52 and the start-upcombustor 54 are provided, the annular second area R2 around the firstarea R1 and where the reformer 46 and the evaporator 48 are provided,the annular third area R3 around the second area R2 and where the heatexchanger 50 is provided, and the annular heat recovery area 106 aroundthe third area R3 as a passage of the oxygen-containing gas (fluid) forrecovery of the heat radiated from the third area R3 toward the outercircumference.

That is, the first area R1 is provided at the center, the annular secondarea R2 is provided around the first area R1, and the annular third areaR3 is provided around the second area R2. Heat waste and heat radiationcan be suppressed suitably. Thus, improvement in the heat efficiency isachieved, thermally self-sustaining operation is facilitated, and simpleand compact structure is achieved. Thermally self-sustaining operationherein means operation where the operating temperature of the fuel cell22 is maintained using only heat energy generated in the fuel cell 22itself, without supplying additional heat from the outside.

Further, the annular heat recovery area 106 around the third area R3achieves heat insulation for suppressing heat radiation and heat wasteadvantageously. Thus, improvement in the heat efficiency is achieved,and thermally self-sustaining operation is facilitated.

In the first embodiment, the fluid supplied to the heat recovery area106 is the oxygen-containing gas before it is supplied to the fuel cellstack 24. Thus, the heat recovery area 106 in the outermost position ofthe FC peripheral equipment 56 can achieve heat insulation forsuppressing heat radiation and heat waste advantageously. Moreover, theoxygen-containing gas is heated suitably before the oxygen-containinggas is supplied to the fuel cell stack 24. Thus, improvement in the heatefficiency is achieved, and thermally self-sustaining operation isfacilitated.

Further, in the fuel cell module 12, the heat recovery area 106 isconnected to the oxygen-containing gas supply chamber 102 a. In thestructure, it becomes possible to suitably heat the oxygen-containinggas before the oxygen-containing gas is supplied to theoxygen-containing gas supply chamber 102 a of the third area R3. Thus,improvement in the heat efficiency is achieved, and thermallyself-sustaining operation is facilitated.

Further, in the first embodiment, as shown in FIG. 3, the reformer 46includes the annular mixed gas supply chamber 78 a, the annular fuel gasdischarge chamber 78 b, the reforming pipes 66, and the secondcombustion gas channel 116 b. The mixed gas is supplied to the mixed gassupply chamber 78 a, and the produced fuel gas is discharged into thefuel gas discharge chamber 78 b. Each of the reforming pipes 66 has oneend connected to the mixed gas supply chamber 78 a, and the other endconnected to the fuel gas discharge chamber 78 b. The second combustiongas channel 116 b supplies the combustion gas to the space between thereforming pipes 66.

The evaporator 48 includes the annular water supply chamber 82 a, theannular water vapor discharge chamber 82 b, the evaporation pipes 74,and the second combustion gas channel 116 b. The water is supplied tothe water supply chamber 82 a, and the water vapor is discharged intothe water vapor discharge chamber 82 b. Each of the evaporation pipes 74has one end connected to the water supply chamber 82 a, and the otherend connected to the water vapor discharge chamber 82 b. The secondcombustion gas channel 116 b supplies the combustion gas to the spacebetween the evaporation pipes 74.

The heat exchanger 50 includes the annular oxygen-containing gas supplychamber 102 a, the annular oxygen-containing gas discharge chamber 102b, the heat exchange pipes 96, and the third combustion gas channel 116c. The oxygen-containing gas is supplied to the oxygen-containing gassupply chamber 102 a, and the heated oxygen-containing gas is dischargedinto the oxygen-containing gas discharge chamber 102 b. Each of the heatexchange pipes 96 has one end connected to the oxygen-containing gassupply chamber 102 a, and the other end connected to theoxygen-containing gas discharge chamber 102 b. The third combustion gaschannel 116 c supplies the combustion gas to the space between the heatexchange pipes 96.

As described above, the annular supply chambers (mixed gas supplychamber 78 a, water supply chamber 82 a, and oxygen-containing gassupply chamber 102 a), the annular discharge chambers (fuel gasdischarge chamber 78 b, water vapor discharge chamber 82 b, andoxygen-containing gas discharge chamber 102 b) and the pipes (reformingpipes 66, evaporation pipes 74, and heat exchange pipes 96) are providedas basic structure. Thus, simple structure is achieved easily.Accordingly, the production cost of the fuel cell module 12 is reducedeffectively. Further, by changing the volumes of the supply chambers andthe discharge chambers, and the length, the diameter, and the number ofthe pipes, a suitable operation can be achieved depending on variousoperating conditions, and the design flexibility of the fuel cell modulecan be enhanced.

Further, the fuel gas discharge chamber 78 b, the water vapor dischargechamber 82 b, and the oxygen-containing gas discharge chamber 102 b areprovided at the side of one end adjacent to the fuel cell stack 24, andthe mixed gas supply chamber 78 a, the water supply chamber 82 a, andthe oxygen-containing gas supply chamber 102 a are provided at the sideof the other end distant from the fuel cell stack 24.

In the structure, the reactant gas immediately after heating and thereactant gas immediately after reforming (fuel gas and oxygen-containinggas) can be supplied to the fuel cell stack 24 promptly. Further, theexhaust gas from the fuel cell stack 24 can be supplied to the exhaustgas combustor 52, the reformer 46, the evaporator 48, and the heatexchanger 50 of the FC peripheral equipment 56 while decrease in thetemperature of the exhaust gas from the fuel cell stack 24 due to heatradiation is suppressed as much as possible. Thus, improvement in theheat efficiency is achieved, and thermally self-sustaining operation isfacilitated.

Further, the oxygen-containing gas discharge chamber 102 b and the fuelcell stack 24 are connected by the stretchable oxygen-containing gaspipes 114. More specifically, each of the oxygen-containing gas pipes114 has a stretchable member such as the bellows 114 a between the upperend ring member 100 b and the stack attachment plate 62. Thus,concentration of heat stress is reduced suitably, and it becomespossible to suppress occurrence of heat strain or the like.

Further, as shown in FIG. 3, the combustion gas flows from the firstarea R1 to the second area R2, and then, flows from the second area R2to the third area R3. Thereafter, the combustion gas is discharged tothe outside of the fuel cell module 12. In the structure, the heat canbe effectively supplied to the exhaust gas combustor 52, the reformer46, the evaporator 48, and the heat exchanger 50 of the FC peripheralequipment 56. Thus, improvement in the heat efficiency is achieved, andthermally self-sustaining operation is facilitated.

Further, the fuel cell module 12 is a solid oxide fuel cell module.Therefore, the fuel cell module 12 is suitable for, in particular, hightemperature type fuel cells such as SOFC.

FIG. 8 is a diagram schematically showing structure of a fuel cellsystem 130 including a fuel cell module 132 according to a secondembodiment of the present invention.

The constituent elements of the fuel cell system 130 including the fuelcell module 132 according to the second embodiment of the presentinvention that are identical to those of the fuel cell system 10including the fuel cell module 12 according to the first embodiment arelabeled with the same reference numeral, and description thereof will beomitted.

As shown in FIGS. 8 and 9, FC peripheral equipment 134 of the fuel cellmodule 132 includes a heat recovery area 136 around the third area R3.As shown in FIG. 9, the heat recovery area 136 is formed independentlyof the oxygen-containing gas supply chamber 102 a (i.e., such that theheat recovery area 136 is in non-communication with theoxygen-containing gas supply chamber 102 a). That is, the holes 108 arenot provided in the lower marginal end portion of the outer member 55.

The oxygen-containing gas supply pipe 110 a of the oxygen-containing gassupply apparatus 16 is directly connected to the oxygen-containing gassupply chamber 102 a.

A hot-water tank 140 is connected to the heat recovery area 136 througha water supply channel 138 a and a water discharge channel 138 b. Forexample, the hot-water tank 140 is used as a water heater for home use.Water is supplied as fluid to the heat recovery area 136.

In the second embodiment, the water in the hot-water tank 140 issupplied to the heat recovery area 136. After the water is heated by thecombustion gas supplied to the third area R3, the water flows throughthe water discharge channel 138 b, and the water is returned to thehot-water tank 140. Therefore, the hot water heated to a predeterminedtemperature is stored in the hot-water tank 140, and the hot water istaken out from the hot-water tank 140 as necessary.

In the second embodiment, water is supplied from the outside of the fuelcell module 132 to the heat recovery area 136. Therefore, it becomespossible to achieve heat insulation for suppressing heat radiation andheat waste from the fuel cell module 132. Further, since the water(e.g., hot water) supplied from the outside of the fuel cell module 132is heated suitably, improvement in the heat efficiency is achievedeasily.

While the invention has been particularly shown and described withreference to preferred embodiments, it will be understood thatvariations and modifications can be effected thereto by those skilled inthe art without departing from the scope of the invention as defined bythe appended claims.

1. A fuel cell module comprising: a fuel cell stack formed by stacking aplurality of fuel cells for generating electricity by electrochemicalreactions of a fuel gas and an oxygen-containing gas; a reformer forreforming a mixed gas of a raw fuel chiefly containing hydrocarbon andwater vapor to produce the fuel gas supplied to the fuel cell stack; anevaporator for evaporating water, and supplying the water vapor to thereformer; a heat exchanger for raising a temperature of theoxygen-containing gas by heat exchange with a combustion gas, andsupplying the oxygen-containing gas to the fuel cell stack; an exhaustgas combustor for combusting the fuel gas discharged from the fuel cellstack as a fuel exhaust gas and the oxygen-containing gas dischargedfrom the fuel cell stack as an oxygen-containing exhaust gas to producethe combustion gas; and a start-up combustor for combusting the raw fueland the oxygen-containing gas to produce the combustion gas, wherein thefuel cell module includes: a first area where the exhaust gas combustorand the start-up combustor are provided; an annular second area aroundthe first area and where the reformer and the evaporator are provided;an annular third area around the second area and where the heatexchanger is provided; and an annular heat recovery area around thethird area as a passage of fluid for recovery of heat radiated from thethird area toward an outer circumference of the fuel cell module.
 2. Thefuel cell module according to claim 1, wherein the reformer includes anannular mixed gas supply chamber to which the mixed gas is supplied, anannular fuel gas discharge chamber to which the produced fuel gas isdischarged, a plurality of reforming pipes each having one end connectedto the mixed gas supply chamber, and another end connected to the fuelgas discharge chamber, and a combustion gas channel for supplying thecombustion gas to spaces between the reforming pipes; the evaporatorincludes an annular water supply chamber to which the water is supplied,an annular water vapor discharge chamber to which the water vapor isdischarged, a plurality of evaporation pipes each having one endconnected to the water supply chamber, and another end connected to thewater vapor discharge chamber and a combustion gas channel for supplyingthe combustion gas to spaces between the evaporation pipes; and the heatexchanger includes an annular oxygen-containing gas supply chamber towhich the oxygen-containing gas is supplied, an annularoxygen-containing gas discharge chamber to which the heatedoxygen-containing gas is discharged, a plurality of heat exchange pipeseach having one end connected to the oxygen-containing gas supplychamber, and another end connected to the oxygen-containing gasdischarge chamber (102 b)chamber and a combustion gas channel forsupplying the combustion gas to spaces between the heat exchange pipes.3. The fuel cell module according to claim 2, wherein the fuel gasdischarge chamber, the water vapor discharge chamber, and theoxygen-containing gas discharge chamber are provided at one end sideadjacent to the fuel cell stack; and the mixed gas supply chamber, thewater supply chamber, and the oxygen-containing gas supply chamber areprovided at another end side distant from the fuel cell stack.
 4. Thefuel cell module according to claim 2, wherein the fluid is theoxygen-containing gas before the oxygen-containing gas is supplied tothe fuel cell stack.
 5. The fuel cell module according to claim 4,wherein the heat recovery area connected to the oxygen-containing gassupply chamber.
 6. The fuel cell module according to claim 2, whereinthe fluid is water supplied from outside of the fuel cell module.
 7. Thefuel cell module according to claim 2, wherein the oxygen-containing gasdischarge chamber and the fuel cell stack are connected to each other bya stretchable oxygen-containing gas pipe.
 8. The fuel cell moduleaccording to claim 1, wherein the combustion gas first flows from thefirst area to the second area, next flows from the second area to thethird area, and then the combustion gas is discharged to outside of thefuel cell module.
 9. The fuel cell module according to claim 1, whereinthe fuel cell module is a solid oxide fuel cell module.